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Spinal muscular atrophy (SMA) is a hereditary condition that affects how the motor neurons in the spinal cord -- the nerves that control the muscles -- get signals from the brain. Without these signals, the muscles weaken and lose their ability to move. With Type 3 SMA (SMA3), also called Kugelberg-Welander disease or juvenile SMA, there’s a pattern of how weakness develops, but the amount of weakness is different for each person.

How Does SMA3 Typically Progress?

Type 3 is usually diagnosed when a child is between 18-36 months, although it can be diagnosed as late as the teen years. Symptoms include:

  • Muscle weakness
  • Trouble walking
  • Frequent respiratory infections

Muscle weakness itself progresses very slowly in this form of SMA. It tends to be symmetrical, meaning it affects both sides of the body. The muscles closest to the center of the body, like the shoulders, pelvis, and upper arms, are usually more affected than those further away, like the lower arms and legs and the hands and feet.

As your child grows, it may be harder for them to keep up with daily activities like climbing stairs. Their muscles shorten around their hips, knees, and ankles. This makes it difficult for them to move around. They may also fall more due to muscle weakness, and they may need help getting up from sitting. About half of kids with SMA3 will stop being able to walk independently by the age of 14.

While most kids with SMA3 have bladder and bowel control, they’ll need help with activities of daily life, like going to the bathroom or getting dressed. They also seem weaker when they’re sick or around times of growth spurts, like puberty.

Later in adulthood, they’re usually less able to get around. Many will eventually need a wheelchair. While they may have problems with breathing and swallowing, that’s usually not until much later in life. They may, however, get sicker from respiratory infections like colds or flu throughout their life due to weaker chest muscles.

What Can I Do to Slow the Progression of My Child’s SMA3?

There’s no cure for any form of SMA, but there are things you can do to that may ease symptoms and potentially slow down the progression of the disease.  

Encourage them to eat a healthy diet. While it’s important to get good nutrition, there’s no evidence that a certain type of diet can help.  

But weight gain can be a problem for people with SMA3, since it can be hard for them to get enough exercise to burn calories. You may need to work with a nutritionist to make sure that your child doesn’t get too many calories. Sometimes, it’s better for them to eat frequent small meals instead of three large ones.

Stay active. It’s important that a child with SMA get as much exercise as they can do comfortably. This will help keep their joints from stiffening up and encourage flexibility. It will also help them maintain circulation and allow them to move around. One good activity is to exercise in a pool warmed to 85 to 90 F.

But while exercise is important, it’s also important not to overdo it. Some experts believe that if a patient with SMA exercises until they’re exhausted, they’ll “burn out” their remaining motor neurons.

Get physical therapy. Physical and occupational therapy can also help people with SMA maintain muscle strength and function. A physical therapist can show you and your child stretches to do to help keep muscles from shortening, which can limit joint movements. If your child needs them, a therapist can help you choose a walker or orthotics to provide support when walking or an electric scooter for them to use for longer distances. The goal is to keep them as mobile as possible for as long as possible.

If your child does develop scoliosis, the therapist can show them correct posture and how to use a brace to help prevent the condition from progressing.

A physical therapist can also teach your child respiratory exercises that can help them breathe if they come down with a respiratory infection like a cold or the flu.

During occupational therapy, your family can learn how to modify activities of daily life so that your child can stay mobile and conserve energy.

Speech therapy can also help with any swallowing difficulties that may crop up later on as the disease progresses.

Keep tabs on their respiratory health. Unlike other forms of SMA, people with type 3 have good breathing function until much later in life. Your doctor will still need to watch them closely, though, for signs of weakening respiratory muscles. 

If they begin to experience respiratory weakening, your doctor can prescribe a portable ventilation machine to use at night.

It’s also important to people with SMA3 to stay up to date on all immunizations, especially flu and COVID vaccines. People with all types of SMA are more likely to develop chest infections if they get a respiratory virus, as they are less able to clear mucus from their lungs.

Take medication. There’s no cure for SMA, but there are drugs that may slow down its progression. They work by raising the levels of survival motor neuron (SMN) protein in the body, which prevents motor neuron cells from shrinking. The three drugs that are FDA-approved for SMA are Evrysdi, Spinraza, and Zolgensma.

Show Sources



Boston Children’s Hospital: “Spinal Muscular Atrophy.”

Muscular Dystrophy Association: “Spinal Muscular Atrophy.”

Cure MSA: “Treating SMA,” “Types of SMA.”

Muscular Dystrophy Australia: “Spinal Muscular Atrophy Type 3.”

SMA Europe: “Type 3 SMA.”

Cleveland Clinic: “Spinal Muscular Atrophy.”

Columbia University Department of Neurology: “Living with SMA: Physical/Occupational Therapy.”